Does Thymectomy Benefit Patients With Anti-MuSK Myasthenia Gravis?
Among patients with anti-muscle-specific kinase (MuSK) myasthenia gravis, thymectomy is not associated with greater likelihood of clinical improvement, according to an analysis of data from a multicenter cohort study.
Although a randomized trial has demonstrated benefit from thymectomy in nonthymomatous antiacetylcholine receptor (AChR) antibody positive generalized myasthenia gravis, observational studies suggest that thymectomy may not be efficacious in anti-MuSK myasthenia gravis. Histologic studies have found that patients with anti-MuSK myasthenia gravis have less hyperplastic thymic tissue, compared with patients with anti-AChR myasthenia gravis.
To evaluate the therapeutic impact of thymectomy in patients with anti-MuSK myasthenia gravis, Katherine Clifford, a medical student at the University of Vermont Larner College of Medicine in Burlington, and colleagues analyzed data from a multicenter, retrospective, blinded review of rituximab treatment in patients with anti-MuSK myasthenia gravis. The primary outcome was favorable outcome on the Myasthenia Gravis Foundation of America (MGFA) Post-Intervention Status (PIS). The researchers defined a favorable outcome as an MGFA PIS score of minimal manifestations or better.
Secondary outcomes included prednisone dose; use of other immunosuppressant medications, IV immunoglobulin (IVIG), or plasma exchange (PLEX) treatment; and Myasthenia Gravis Status and Treatment Intensity (MGSTI).
Baseline characteristics were similar between patients with anti-MuSK myasthenia gravis who received thymectomy (n = 26) and those who did not (n = 29), including treatment with rituximab (42% vs 45%). Median follow-up was more than three years.
At last visit, 35% (nine of 26) of patients who received thymectomy had a favorable outcome, compared with 55% (16 of 29) of patients who did not receive thymectomy. In addition, 69% of patients who received thymectomy were taking prednisone, compared with 41% of patients who did not receive thymectomy (median dose, 10 mg/day vs 0 mg/day).
“After controlling for rituximab, baseline prednisone, and final IVIG/PLEX treatment, thymectomy was not associated with greater likelihood of favorable clinical outcome, but broad confidence intervals cannot exclude therapeutic effect (odds ratio, 0.43),” the investigators reported.
“The recent MGTX trial clearly demonstrated the benefit of thymectomy for patients with AChR antibody positive myasthenia gravis,” said A. Gordon Smith, MD, Cochair of the AANEM Annual Meeting Program Committee. “Ms. Clifford and her colleagues now provide compelling data suggesting thymectomy may not be effective in MuSK-positive myasthenia gravis.”
The study’s follow-up is long enough for the findings to be clinically “relevant to all physicians treating myasthenia gravis,” said Robert W. Irwin, MD, Cochair of the AANEM Annual Meeting Program Committee.
What Are the Clinical, Laboratory, and Electrodiagnostic Features of Zinc Deficiency-InducedPeripheral Neuropathy?
Patients with zinc deficiency-induced peripheral neuropathy may present with paresthesia, gait abnormalities, sensory deficits, reduced tendon reflexes, an abnormal Romberg test, and increased CSF protein, according to a study.
Recognition of the features of zinc deficiency-induced peripheral neuropathy may help neurologists diagnose the disorder and manage patients, researchers said.
“Zinc, an essential trace element, plays a critical role in maintaining normal structural and functional conditions in the body,” said lead author Favio C. Bumanlag, Chief Technologist in the Department of Neurology at the Lewis Katz School of Medicine at Temple University in Philadelphia. “Peripheral nerves are susceptible to damage when zinc deficiency occurs.... Recognition of [zinc deficiency-induced peripheral neuropathy] will help physicians and technologists effectively manage patients.”
To study the clinical and electrophysiologic features of zinc deficiency-induced peripheral neuropathy, Mr. Bumanlag and Jin Luo, MD, PhD, Professor of Neurology and Pharmacology at Temple University, retrospectively reviewed charts in their neuromuscular clinic and EMG laboratory database to identify patients with peripheral neuropathy and zinc deficiency. They included charts from between January 1, 2015, and December 31, 2017, in their review. They excluded patients with abnormal copper levels.
Mr. Bumanlag and Dr. Luo obtained information about patients’ clinical presentations, past medical histories, BMI, neurologic examinations, and laboratory results. They also examined patients’ needle electromyograms and nerve conduction studies.
In all, they identified 12 patients with peripheral neuropathy and zinc deficiency. Patients had a mean age of 55.1. Six were female. Patients’ mean zinc level was 52.5 μg/dL, with a range of 37 μg/dL to 58 μg/dL (reference, 56–134 μg/dL). Mean copper level was 107.6 μg/dL, with a range of 84 μg/dL to 173 μg/dL (reference, 72–166μg/dL). Eleven of the 12 patients had received an electrophysiologic evaluation.
Notable findings in presentation included paresthesia in 75 and gait abnormalities in 42%. One patient was obese (8%), and three patients had diarrhea (25%). Neurologic examination showed sensory deficits in 83%, reduced tendon reflexes in 67%, and an abnormal Romberg test in 67%. Four of five patients had increased CSF protein. Electrophysiologic evaluations showed features of demyelinating peripheral neuropathy (28%) and distally active denervation in the lower extremities.
“Zinc participates in more than 200 enzymatic reactions,” said the researchers. “Unfortunately, zinc deficiency-induced peripheral neuropathy is often misdiagnosed or delayed in diagnosis. Literature on zinc deficiency-induced peripheral neuropathy is sparse.”